The fundamental element of the wheel-on-rail guidance system. The inner edge of each wheel is shaped to a larger diameter than the wheel tread resting on the rail to act as a guide for the wheel set. The two flanges of the wheels on an axle guide the wheel set to follow the route of the track. A characteristic squealing sound can often be heard on sharp curves as the outer wheels' flanges slice along the inner edges of the rails.

As distinct from bullhead rail, which is attached to the sleepers with chairs and keys, flat-bottomed rail was originally laid directly on the sleepers and held by spikes, the heads of which overlapped the base of the rail. (Even after 1945 many Continental main lines still used this form of track.) Modern flat-bottomed track is more sophisticated – the rail is laid on base-plates attached to the sleepers and held by spring clips.

Arrangement of tracks at a major junction where one or more running lines were carried over others by means of an embankment and overbridge rather than crossing on the level, thus avoiding conflicting movements. The first flyover built to replace a flat junction was at Weaver Junction, brought into use in November 1881; it carried the new up Liverpool main line via Runcorn, after the building of Runcorn bridge, over the up and down main lines. Other important flyovers were at Vauxhall (Birmingham), Rugby Clifton Road and Liverpool Edge Hill. Lack of space prevented the construction of flyovers at other busy locations where they would have been beneficial. A few more flyovers were in fact constructed in later (BR) years, including Rugby North (No.7 box) and Bletchley, thelatterbeing something of a white elephant.

Cottages provided by the railway company to house staff who might be called on for fog-signalling duties in the close vicinity. The purpose was to avoid delays to the service while the men could be contacted and travel to their assigned locations. Some of these cottages survive today.

During fog and falling snow (when visibility was less than 200 yards) special signalling regulations came into force. A person, usually a railwayman normally employed in some other capacity such as platelayer, was stationed at each distant signal (and certain other signals) and placed detonators on the rail as an audible warning to drivers when the signal arm was “on”. In the days when coal was the only domestic and industrial fuel, dense and prolonged fogs were common even into the 1950s, especially in urban areas in winter.

Metal cylinders filled with very hot water or chemicals at stations and placed on the floor of coaches not fitted with any form of heating. Steam and electric heating rendered them obsolete by the mid 1920s.

The act of blocking one line with a movement or stationary train on another line. Usually occurs when train has not pulled far enough into a siding, or when shunting wagons and the running line is used as a head shunt.